There are two things happening, both because of the negative externalities that traditional sources produce, but aren't factored in to prices. One is subsidies,

There are two things happening, both because of the negative externalities that traditional sources produce, but aren't factored in to prices. One is subsidies, the other is source prioritization both of which favor renewables. Plants that can provide that peaker gap on windless+cloudy days should be rewarded by the market by very high kwh purchase prices, but that's all. The current benefits that renewables receive are aligned with the true costs. Alternatively you could replace the prioritization and subsidies with a heavy carbon tax on traditional sources but the result would be the same.